The Mouse Breeding Core (Core C) will generate, house, and maintain the final breeders needed to obtain the single and combined gene targeted and transgenic mice needed for all projects of the Program Project Grant (PPG). Once obtained, these animals will be turned over to individual investigators of the projects of the PPG for large-scale breedings to generate the required numbers of animals for the studies proposed. The animal complex is directed by a veterinarian and board certified veterinary pathologist, Dr. Mark A. Suckow, who establishes the policies regarding animal care and breeding. An associate director manages day-to-day supervision of the ten technologists who care for the animals and establish the requested breedings. Three of these latter individuals are assigned to animals of the W.M. Keck Center for Transgene Research that will be used in the investigations of the current PPG. The responsibilities of this core will be to generate appropriate mice that when bred by investigators will lead to a high statistical probability of obtaining the specific animals needed for the studies. Given the complexities of the genetic strains of the final animals in these projects, strains with low probabilities of generating the final animals will be first required. Core C will assume responsibility for this latter task. The aims of this core are to generate at a minimum: 1) X[+/-] or X[-/-] (when mice with this genotype are able to survive and breed) mice and X+/-/Y-/- (where Y is a second gene) or X-/-/Y-/- for large-scale breedings to generate animals required for Project by Castellino; 2) APC[Min+/-o]/X+/- (or X-/-, if they survive and breed) mice for large-scale breedings for Project by Ploplis; and 3) to generate sufficient numbers of WT and FX+/- breeders for Project by Rosen.